1. Field of the Invention
The present invention relates to lithium metal oxide compositions as well as electrochemical devices utilizing such compositions and, in particular, to lithium-magnesium nickel oxide compositions suitable as components of lithium-ion electrochemical devices.
2. Description of Related Art
Rechargeable lithium and lithium-ion batteries can be used in a variety of applications, such as cellular phones, laptop computers, digital cameras and video cameras, and hybrid electric vehicles etc., due to their high energy density.
Commercially available lithium-ion batteries typically consist of graphite-based anode and LiCoO2-based cathode materials. However, LiCoO2-based cathode materials can be expensive and typically have relatively low capacity, approximately 150 mAh/g.
Alternatives to LiCoO2-based cathode materials include LiNiO2-based cathode materials, which can be less expensive. Typical LiNiO2-based cathode materials can include compositions having a formula LiNi0.8Co0.2O2 or LiNi0.8Co0.15Al0.05O2. These materials are relatively more expensive than cobalt-free LiNiO2-based cathode material because of the relatively higher cost of cobalt relative to nickel. Furthermore, LiNiCoO2-based cathode materials usually have lower safety, cyclability, and first cycle efficiency over LiCoO2-based cathode materials because of the lower structural stability and higher surface reactivity of LiNiO2 type cathodes.
Li(Ni, Co)O2-based cathode materials have also been disclosed. For example, Lecerf et al., in U.S. Pat. No. 4,980,080, disclosed a process of making a cathode material for a secondary battery having a formula LiyNi2-yO2 or Li1-xCoxO2. Xie et al., in U.S. Pat. No. 5,750,288, disclosed modified lithium nickel oxide compounds for electrochemical cathodes and cells based on LixMyOz materials, where M is a non-transition metal selected from the group consisting of aluminum, gallium, tin and zinc. Mayer, in U.S. Pat. No. 5,783,333, disclosed a LisNiyCOzMnO2 material. Mayer also disclosed, in U.S. Pat. Nos. 6,007,947 and 6,379,842, cathode materials having a formula LixNiyCOzMnO2 or LixMn2-rM1rO4 where M is a metal selected from the group consisting of aluminum, titanium, tungsten, chromium, molybdenum, magnesium, tantalum, silicon, and combinations thereof and M1 is one of chromium, titanium, tungsten, nickel, cobalt, iron, tin, zinc, zirconium, silicon, or a combination thereof. Kumta et al., in U.S. Pat. No. 6,017,654, disclosed cathode materials having a formula Li1+xNi1-yMyNxO2(1+x) and LiN1-yMyNxOp where M is a transition metal selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, and aluminum and N is a Group II element selected from the group consisting of magnesium, calcium, strontium, barium, and zinc. Sunagawa et al., in U.S. Pat. No. 6,040,090, disclosed a positive electrode material based on Li—Ni—Co—Mn—O2. Peres et al., in U.S. Pat. No. 6,274,272, disclosed an active cathode material having a formula LiLNi(I-C-A-M) CoCAlAMgMO2. Gao et al., in U.S. Pat. No. 6,277,521, disclosed a lithium metal oxide material containing multiple dopants with a formula LiN1-xCOyMaM′bO2 where M is a metal selected from the group consisting of titanium, zirconium, and combinations thereof and M′ is a metal selected from the group consisting of magnesium, calcium, strontium, barium, and combinations thereof. Mao et al., in U.S. Pat. No. 6,071,649, disclosed LiCoO2-coated LiNiO2 or Li(Ni,Co)O2 materials. None of these disclosed Li—Mg—Ni—O2-based cathode materials.
Matsubara et al, in U.S. Pat. No. 6,045,771, disclosed a cathode material having a formula Liy-x1Ni1-x2MxO2 where M is a metal selected from the group consisting of aluminum, iron, cobalt, manganese, and magnesium, x=x1+x2, 0<x1≦0.2, 0<x2≦0.5, 0<x≦0.5, and 0.9≦y≦1.3.
Multiple companies are also commercially fabricating cathodes utilizing materials with a general formula LiNiCoMO2. TODA (earlier Fuji Chemical) manufactures products CA5, CA1505N, and NCA. Honjo-FMC and Nichia (both of Japan) also provide nickel-cobalt-based cathodes. These products typically suffer from low safety properties, and relatively low rate capability.